Compensation for variations in phase change



June 17, 1941.

POWER SYSTEM A AAAA N. MONK COMPENSATION FOR VARIATIONS IN PHASE CHANGE F iled Feb. 21, 1939 POWER SYSTEM 3 PHA SE COMPENSA T0)? A l mar CIRCUIT POWER SYSTEM A FIG. 7

POWER SYSTEM 8 n f PILOT CIRCUIT loo 2 Sheets-Sheet 2 MECHANISM ADJUST/N6 H T0 LOCAL CONTROL APPA/PAHIS INVENTOR IV. MONK ATTORNEY v Patented June 17, 1941 2,246,058 COMPENSATION FOR VARIATIONS 1N PHASE CHANGE Newton Monk, New York, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application February 21, 1939, Serial No. 257,674

9 Claims.

This invention relates to a method and means for substantially reducing variations in the phase characteristic of a transmission circuit particularly at any one frequency and is applicable more especially to a cable circuit.

An object of this invention is to provide a new and improved method and means for substantially reducing Variations in the phase characteristics of a cable circuit particularly at any one frequency due to varying weather conditions or other causes.

Another object is to provide a method and means for improving transmission characteristics of cable circuits.

A further object is to provide a pilot'circuit, in which variations in phase change are substantially eliminated, for use in measuring the phase relationship of the current at different points in an electrical system.

each end of the circuit in a specific impedance as described below. The method is applicable to those circuits for which the shunt impedance of temperature changes; in other words for cases in which the effect of leakage is very small or negligible. This is true for transmission of currents of frequencies up to the order of several thousand cycles over cable circuits of som length.

A description of an embodiment chosen for illustrating this invention in which reference is made to the accompanying drawings, follows:

Fig. 1 is an equivalent T-network of a cable circuit;

Fig. 2 is an equivalent T-network ofthe cable circuit of Fig. 1 showing the impedance changed due to varying weather conditions or the like:

Fig. 3 shows an application of terminating impedances according to the principles of this invention for compensating for variation in phase characteristic of a circuit when an alternating current is transmitted thereover;

Fig. 4 shows an application of-this inventio for measuring by means of a pilot line the phase difierences between voltages at two points;

Figs. 4A and 4B show different arrangements for connecting an alternating voltage source to the pilot line arrangement of Fig. 4;

Fig. 5 shows an application of this invention for measuring by means of a pilot line the phase differences between voltages at two points in which compensation is introduced for the change in phase introduced by the pilot line itself;

Fig. 6 shows an application of this invention for measuring by means of a pilot circuit the phase angle diiferences between different points of a power system or systems; and

Fig. '7 shows an application of this invention to power transmission for automatically maintaining the current at different points of the system or systems in phase.

The underlying principles of this invention are first described by referring to the equivalent T'- network included in Figs. 1 and2; while certain applications are described in connection with subsequent figures.

Fig. 1 shows a cable circuit reduced to its' equivalent T-network for a given weather condition. The network is assumed to be connected to a generator E of any impedance Zr and terminated in an impedance also of value Z'r. The impedance Z1 which is one-half of the series impedance of the network is equal to R +jL w where R1 is the total resistance of the circuit, L1 its total inductance, and w=21r times the frequency. Z2 represents the shunt impedance of the equivalent T-network and is equal to in which G1 is the leakage conductance of the circuit, and C1 its capacitance.

Fig. 2 represents the equivalent T-network of the same circuit under a different weather con dition in which the series and shunt impedances may be considered to have new values Z1 and Zz, resulting from changes in the fundamental constants of the circuit. It is a well-known fact that the leakage conductance G of a well insulated cable circuit enclosed in a protective sheath is very small. The term G can, therefore, be neglected in comparison to the term Cw. Consequently, the values of the shunt impedances Z2 and Z'2 of the networks reduce to jCHw jC" w respectively. Furthermore, for changes in weather, including temperature changes, the capacitance C of a cable circuit will not change materially. Thus the shunt impedance Z'z of the network of Fig. 2 will be substantially equal to that of the original network of Fig. 1 and Z'z wvill be substantially equal to Z2.

The ratio between the currents i2 and i: determine the variation in phase change. These currents may be expressed as follows:

If the value of Z1: is now made very large the impedances Z1 and Z1 (which will be'onlyslightly difierent from Z1), which represent one-half of the total series impedance of the equivalent T'-networks o Fig. 1 or Fig.2, may be neglected" and the right hand side of Equatio'n4 reducesto unityindicating that-the phase-change between the two currents is zero.

It is obvious from Equation 4 that; the value of' ZT may be any value largein comparison with Z1 aridfmay bebither a resistance or a reactance. However; it must not be so great that the'attenu ation "becomes excessive. In order to determine the best value for the impedance ZT- the ex; pression' for I the attenuation; that is; the'relation between the currents i1 and 2'2 may bewritteh Z2l. ,ir I. ifzl+z +zr (5) which neglecting Z1 reduces to ream this 1 expression and themaximumwalue I of--- attenuation, whichmaybeallowedQthe value for Z'r may be determinedr The results which may be obtained with this method for reducing the variations in phase change of the circuit will,=of course, depend upon the'relative values of Z1, one-half the serie's-im-- pedance of the equivalent T-network,- and the terminating imp'edances Zr.- If the-attenuation is permitted to'be large. the value of Z'r can be made very large and the -;variation in the phase change can be eliminated -for all practical purposes.

This me'th'o'd ishpplied in the followin'gex ample to an actual cable ircuit' at' 60c'ycles tak ing a 'nonaloaded' 19 -gau'ge'cabl'e circuit 10 miles in leiigtlr'l' The fundame'ntal constants for such viding a circuit of substantially constant phase Considering a temperature change from- 68 ture variation foi' underground "cable, the; values f; for the fundamental constants' 1:11:32" are as' follows: v

R=78.2ohms per mile L=.00106- henry per mile 0:.0654 mfd. per mile" G=.05 micromho per mile It is assumed 'that the leakage G isequal to0.1 micromho pep-mi-Ieand that itchanges 50 per cent over the, temperature range from 68 F. to

Employing these fundamental constants the equivalent T-networks for a 10-mi1e circuit work out to have the following impedance values:

If an attenuation of 20 db is permitted the 7 maximum value of resistance or reactance which may be employed for Z! is from Equation 5 about 40,000 ohms.

Substituting the above values for Z1, Z1, Z2, Z2 and Zwfinto Equation 3 we find that the variationin 'phasechange' will be as follows:

Variation Z'r in phase change I r Degrees 40,000 ohms 0. l8 +i40,000 ohm's. 20 j40,000'ohms 14 This compares with a total variation in phase change of about 1L0 degree which would obtain if the circuit were terminated in characteristic 7 30 lmpedance.

The leakage in such a circuit may, however, be considerably different from 0.1 micromho per mile at 68F. Furthermore, the change in leakage over the temperature rangeassumed may be considerably less than 50 per cent.- If either the leakageris less than that assumed or the change in leakageis less than 50 per cent the variationin the-phase change'will beless than the com.

variations'in the phase characteristics of a cir-- cuit when an alternating current is transmitted Thevalues'of the impedances Zr at each end of the: line are so determined that when the voltage of an alternating current of a given frequency generated by source E isimpressed upon the line, the variation'in phase change caus'edby the transmission line is'neutralized or reduced. Such.

a compensated line'may be used by itself or as a pilot circuit in conjunction with other circuits or systems examples of which are subsequently described herein;

The method and means described above of pro characteristic"may be utilized in various ways, a number' ofillustr'ative applications of thisinvention being described below.

for comparing by ine'ans'of a pilot circuit, such as a telephone-line, the phase angle between two Voltages V rand Vz' originating at'difierent sources or stations'Agand B: The voltage'Vi is trans- :mitted from station A 'over the pilot line l00to station B at the distantend of the pilot line where 7 another voltage V2 isto be compared withthe voltage Vr by means of'a phase anglemet'r 200,

to determine the difierence in phase between the two Voltages V and Va The voltage Vrgen'.

Fig.4 shows" an application or *this invention" erated at station A is impressed upon the pilot 1inel00 and transmitted to the distant end at stationB where the voltage is taken off from the pilot line through series resistances R1 and R2 which must have a high resistance in comparison with the impedance of the line and of the terminating impedances ZT. In order that the phase angle between the voltages V1 and V2 may be obtained from the readings of the phase angle meter 200, it is of course necessary to correct for any change in phase of voltage V1 which may be introduced by the line I00. This may be accomplished by measuring the phase change caused by the line itself between proper impedances ZT at each end of the line. This phase change caused by the line must then be subtracted from the indication given by the phase angle meter in order to obtain the true phase difference between the voltages V1 and V2. The phase change caused by the line itself may be measured by any of the well-known methods, for example, that shown in W. P. Mason Patent 1,684,403, issued September 28, 1928. The phase change caused by the line itself will change with weather variations and the like and this may be minimized in accordance with this invention by terminating the ends of the line with similar impedances Zr, the value of which may be calculated as explained above, particularly in describing Figs. 1 and 2.

Figs. 4A and 4B show alternative arrangements for connecting the source of alternating voltage to the line circuit I00. In Fig. 4A the coupling is a transformer so designed that the impedance ZT looking into the line side of the transformer is of the proper value for terminating this end of the line for effecting the desired reduction of phase variations therein. In Fig. 4B the coupling is also a transformer and in addition separate impedances are inserted in the line to build up the impedance ZT looking into the line side thereof to afford the proper impedance.

Fig. 5 also shows an application of this invention for comparing by means of a pilot line, the phase angle between two voltages V1 and V2, at stations A and B, respectively, in a manner similar to that described in Fig. 4 but without the necessity of separately measuring the phase change caused by the line itself, since in this arrangement a phase compensator 300 is employed to compensate for phase changes in the line. The action of the phase compensator 300 is such that the phase angle meter 200 is held at zero indication when the voltages V1 and V2 are in phase. The phase compensator may consist of a network composed of one or more of the following elements, resistances, inductances, and capacitances. The design of such networks is well known in the art. See, for example, H. Nyquist Patent 1,770,422, July 15, 1930. With this arrangement wherein the phase change introduced by the line is corrected the phase angle meter always directly indicates the phase angle between voltages V1 and V2. The general description of Fig. 4 is obviously applicable to this figure.

Fig. 6 shows another application of this invention wherein it is employed for measuring the phase angle difference between two different power systems or two different points on the same power system. The two different power systems A and B or the two different points on the same power system are connected through suitable coupling means by a pilot circuit for comparing the phase relationship of the two systems or points on the same system. The power systems, or system, are shown as three-phase systems and the pilot circuit I00 is connected at two selected points A and B by means of suitable coupling elements across one phase of the power line. Measuring the phase difference between the two points in one phase of a polyphase system may be sufficient when the several phases are substantially balanced, but if phase angle measurements for the other phases of a polyphase system are desired, they may be made for the other phases of the power system either by employing a pilot circuit for each phase or by having switching devices for synchronously switching the pilot circuit connections from one phase to another of the power system. The ar rangement here shown is similar to that of Fig. 5 for measuring the phase angle between two sources of voltage and is here applied to measure the phase angle between the two points on one phase of the power system or systems A and B, irrespective of the location of the source or sources of power. The series resistances R1 and R2 must be high in comparison with the terminating impedance ZT at each end of the pilot circuit. The phase compensator 300 compensates for any phase displacement caused by the pilot circuit and consequently the readings of the phase angle meter 200 show directly the phase difference between the voltages of the different power systems.

Fig. '7 shows a further application of this invention as applied to power transmission for automatically maintaining two different power systems or two different points in the same power system in phase. The arrangement here shown is similar to that of Fig. 6 but employs in addition automatic means for adjusting the phase relationship of one system to that of another system so that they may be automatically maintained substantially in phase with one another. A differential relay arrangement 400 is here substituted for the phase angle meter measuring arrangement shown in Fig. 6 which automatically operates when there is a difference in phase between the two systems A and B. When a relative phase change occurs in one direction, the relay closes a circuit which operates an adjusting mechanism 500 connected with local control apparatus to cause a shift in the proper direction of the phase in the local system and when the relative phase change is in the opposite direction, the relay closes another circuit which causes a shift in the opposite direction of the phase of the local system, thereby automatically causing a phase change in the local system to substantially eliminate the phase difference between the systems. The differential relay arrangement 400, as here shown, consists of two vacuum tubes 40! and 402 in push-pull arrangement and so connected that the output circuit of each tube controls the energization of one side of a diiferential relay 4| 0 which in turn operates the phase adjusting mechanism 500, and thus maintains a balance in the phase relationship of the systems. The input circuits of this differential relay arrangement are connected by suitable coupling transformers with the pilot circuit I00 interconnecting the power systems A and B and with a local circuit associated with the power system B. The adjusting mechanism 500 which may be mechanically connected to the local control apparatus for adjusting the phase relationship of thelocal system to that of the other sys tem may be of any suitable type such as is now used and mechanically operated for changing the phase relationship of a power system 'withthat off another such systemx Fig; 7; as above-stated, relates primarily .to the" automatic :control' ofthe relationship rather than-to themechanism operating the local control apparatuswThe adjust ing mechanism may be of any suitable typesuch, forexample; as'that' shown in-Patent 1,703,142 to- E: 1. :Green, especially Fig. 2a 'whichirelay 32 may'ccorrespond. to plication.

'All of these applicationslarexmadeapracticable I substantially constant byzproviding a circuit 'of phase relation. This invention may phase characteristic is required :170 be substantially constant. 1-

relayl H) 'of the: present apbe: i-applied' to '7 any line, within the limits outlined abova for which the A division of this application has "been filed 'as serialsNo. 310,129, filed December 20;"1939, for

Compensation for variations in phase change. A

While this invention has'been disclo'sed-asem-' bodied 'in certain particular forms;-:it is to 'be understood'th'at it is'notl-imited 'to' such forms but" is capable of embodiment in other 1 formswithout departing from the spirit and scope of pl' nded claims.

What-is-claimedis:" V.

1. A method of minimizing variations =in the phase change in alternating current being trans mitted between points in a circuit which consistsin terminating both ends of: saidcircuit with substantially equal impedances (ZT) havingvalueslarge in comparisonzwith one-halfhthe: series'impedance, of theequivalent T-network' v2. A 1 method of .minimizing "variations. in i the V I phase: change in alternating currentbeing transe' I mitted between pointsin a "circuit, which con-1' sists' 'in terminating bothends of isaid circuit with -fequal resistances having values: large in comparison with one-half the seriesiimpedancei of the equivalent T-network -.of. saidiicircuit (Zrand-Z"1). V

3..,A method of minimizingvariations in the phase-change" in alternating current being transmitted 'between points in-a CiI'CHit WhiCh consists in terminating both ends ofsaid circuit with equal reactances having values large in comparisomwithone-half the series impedancewof the equivalent F-network oftsaidcircuitim and Zi) 4. A 1 method of minimizing variations the phaserchan'ge in alternating current beingetrans mittedbetween' points in a circuit, which con-- sistsinterminating both ends of said circuit with equal positive reactances havingvalues large in comparison with one-half theseries impedance'of the-equivalent- T-network'rofsaid 'circuit (Z1 and Z.1 a a 5; A method -of' minimizing: variations in the phase change. in alternating current beingrtrans mitted between points in a circuit, which-contsists in terminating both ends of saidcircuit'with equal negative. reactances havingvalues large in comparison: 'withone-half the series impedance of the equivalent T'-network of said 'circuitizi and Z1). A v

6; Means for compensatingfor variations in i phase change in .an electrical circuit which in-- eludesterminating each end of the circuit'with substantially equal impedances large in comparl son with zone-half the series impedance of theequivalent T-network for said circuit.

7. Means "for compensating for-variations in phas change in'an electrical circuit which in-" cludes terminating each-end ofthe circuit with substantiallyequal resistances large in comparison with one-half the series impedance of the equivalent T-networh for saidoircuit;

8. -Means for compensating for variations" in phase change-in an electrical circuit which includes terminating each ,end of the circuit with substantially equal reactances large in comparison with one-half'therseries impedance of the equivalent T-network for saidcircuit.

9. Atransmission line over which alternating current-is transmitted, the current undergoing a change-in phase between separatedpoints in said 1 line, said phasegchange; normally varying With-f variationcin the atmospheric conditions surrounding said line, and means to maintain said phase change-substantially constantregardless of variation'in saidatmospheric conditions," said means comprising substantially equal-impedancesc at. :eachend of the line; each'impedance being large in comparison with one-half the series impedance'of i the equivalent T-network of theline. v

NEWTGNMONK. 

